The experimental transition frequencies are from
(1) G. Cazzoli, L. Cludi, M. Contento, and C. Puzzarini, 2008, J. Mol. Spectrosc. 251, 229.
The purely K-dependent parameters (A and D_K), needed to obtain reasonable intensities, were taken from CH₃CCH;
(2) H. S. P. Müller, P. Pracna, and V.-M. Hornemann, 2002, J. Mol. Spectrosc., 216, 397.
Some higher order spectroscopic parameters were estimated from the main species. The calculated transition frequencies should be reliable throughout.
The dipole moment was assumed to agree with that of the main species, see e064507.cat.